Approaches to Immunopathology

Immunopathologic studies can be performed on paraffin or frozen tissue, with comparable sensitivity and specificity, although frozen immunofluorescence is generally considered to be the gold standard. The ISHLT WF allows laboratories to use whatever method they prefer based on their capabilities and individual preferences, but it is critical to have appropriate staining controls.

There are important logistic considerations with immunofluorescence, since the biopsy tissue must not be placed in formalin. Since the frozen tissue is separated from the other pieces examined by routine histology, reviewing the frozen section H&E from this piece should not be overlooked. The specific antibody staining panels differ for each method and the ISHLT WF has outlined required and optional sets of stains for each (see IHC Table and IF Table).

Immunopathologic diagnosis

Immunohistochemistry (IHC) for paraffin-embedded tissue and immunofluorescence (IF) for frozen-tissue will be treated separately as they entail different antibody panels and a different mode of interpretation.

Low and High Power Examination

Like routine histology, an algorithmic approach to immunostain interpretation is helpful. An approach based on scanning/low power (x20-40) followed by high power (x200-400) is suggested.

The first low power biopsy assessment helps:

  • Ensure adequate myocardial tissue and section quality
  • Assess overall pattern of staining (focal, multifocal, diffuse)
  • Identify areas to evaluate on higher magnification and areas of artifactual staining to avoid

    High power examination helps:

  • Assess intensity, pattern (granular versus homogeneous/linear), and completeness of circumferential capillary staining for complements
  • Localize CD68+ macrophages (inside or outside the capillary walls)
  • Forward to Immunohistochemistry.
  • Back to Histopathology.
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